With the increasingly extensive application of mobile communications, there are higher requirements on a communications capacity and communications quality. A remote electrical tilt antenna with an adjustable downtilt can implement good coverage, and reduce mobile communication interference between cells. A phase shifter is an important part of the remote electrical tilt antenna, and a phase adjustment range of the phase shifter has great impact on an effect of standing wave match. In addition, as a quantity of antenna ports in a radio frequency system of a base station increases, a requirement for miniaturization of the phase shifter becomes more urgent.
The phase shifter changes an output phase at an output port by adjusting a length of signal transmission from an input port to the output port. In the prior art, to improve electrical performance of the phase shifter and expand the phase adjustment range, the length of signal transmission from the input port to the output port always needs to be able to increase or decrease within a relatively wide range, and a size of the phase shifter is increased.